Dr. Raymond E. Zimmerman, 63, of 108 Annwood Road in Palm Harbor pleaded guilty to a single count of taking an illegal kickback for referring patients to Clearwater Clinical, a medical lab that paid kickbacks "as a regular part of company practice," according to court documents.

Federal prosecutors have charged 14 doctors in the case, as well as James McKeown Sr., founder of the company; his son, James McKeown Jr., who was involved in the day-to-day operations of the lab; and Vincent "Vinny" Gepp, the lab manager. All the physicians still retain their licenses. The FBI has characterized Clearwater Clinical as the "largest payor of illegal kickbacks in the Pinellas County area," and says the lab reaped $6.5-million in Medicare reimbursements in 1997 alone as a result of the illegal activity.

Zimmerman, who listed his income in court documents as $10,000 a month, was indicted in August, along with another Pinellas physician, Dr. Efstathios Mark Varidin, and charged with conspiracy and soliciting or receiving payments in the referral of Medicare patients to Clearwater Clinical.

The two men were accused of taking $21,000 in kickbacks for referrals from 1995 to 1997, which netted Clearwater Clinical $158,240 in Medicare reimbursements.

Varidin has pleaded not guilty to the charges.

Zimmerman, as part of a plea agreement, admitted he entered into an fraudulent contract with Clearwater Clinical to act as a "testing review officer" for the lab for payments of $1,500 a month. Under questioning by a federal magistrate Tuesday, Zimmerman said he received the $1,500 payments for referring Medicare patients to the lab and never actually performed any work as a testing review officer.

Zimmerman faces a maximum of five years in prison, a fine of $250,000 and restitution to the Health Care Financing Administration of $21,000.

In return for Zimmerman's cooperation with the federal investigation, the U.S. Attorney's Office agreed to drop other charges in the indictments and to make a recommendation for leniency at sentencing.

The investigation of Clearwater Clinical Laboratory began with tips from informers and an FBI raid of the facility in 1998. Authorities say the records seized revealed a massive conspiracy to pay kickbacks for patient referrals and an array of phony contracts used to hide the illegal payoffs.